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Mitsuhiro Murayama - One of the best experts on this subject based on the ideXlab platform.
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investigating the dislocation reactions on σ3 111 Twin boundary during Deformation Twin nucleation process in an ultrafine grained high manganese steel
Scientific Reports, 2021Co-Authors: Chang Yu Hung, Yu Bai, Tomotsugu Shimokawa, Nobuhiro Tsuji, Mitsuhiro MurayamaAbstract:Some of ultrafine-grained (UFG) metals including UFG Twinning induced plasticity (TWIP) steels have been found to overcome the paradox of strength and ductility in metals benefiting from their unique Deformation modes. Here, this study provides insights into the atomistic process of Deformation Twin nucleation at Σ3{111} Twin boundaries, the dominant type of grain boundary in this UFG high manganese TWIP steel. In response to the applied tensile stresses, grain boundary sliding takes place which changes the structure of coherent Σ3{111} Twin boundary from atomistically smooth to partly defective. High resolution transmission electron microscopy demonstrates that the formation of disconnection on Σ3{111} Twin boundaries is associated with the motion of Shockley partial dislocations on the boundaries. The Twin boundary disconnections act as preferential nucleation sites for Deformation Twin that is a characteristic difference from the coarse-grained counterpart, and is likely correlated with the lethargy of grain interior dislocation activities, frequently seen in UFG metals. The Deformation Twin nucleation behavior will be discussed based on in-situ TEM Deformation experiments and nanoscale strain distribution analyses results.
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a correlation between grain boundary character and Deformation Twin nucleation mechanism in coarse grained high mn austenitic steel
Scientific Reports, 2021Co-Authors: Chang Yu Hung, Yu Bai, Tomotsugu Shimokawa, Nobuhiro Tsuji, Mitsuhiro MurayamaAbstract:In polycrystalline materials, grain boundaries are known to be a critical microstructural component controlling material’s mechanical properties, and their characters such as misorientation and crystallographic boundary planes would also influence the dislocation dynamics. Nevertheless, many of generally used mechanistic models for Deformation Twin nucleation in fcc metal do not take considerable care of the role of grain boundary characters. Here, we experimentally reveal that Deformation Twin nucleation occurs at an annealing Twin (Σ3{111}) boundary in a high-Mn austenitic steel when dislocation pile-up at Σ3{111} boundary produced a local stress exceeding the Twining stress, while no obvious local stress concentration was required at relatively high-energy grain boundaries such as Σ21 or Σ31. A periodic contrast reversal associated with a sequential stacking faults emission from Σ3{111} boundary was observed by in-situ transmission electron microscopy (TEM) Deformation experiments, proving the successive layer-by-layer stacking fault emission was the Deformation Twin nucleation mechanism, different from the previously reported observations in the high-Mn steels. Since this is also true for the observed high Σ-value boundaries in this study, our observation demonstrates the practical importance of taking grain boundary characters into account to understand the Deformation Twin nucleation mechanism besides well-known factors such as stacking fault energy and grain size.
Y T Zhu - One of the best experts on this subject based on the ideXlab platform.
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grain size effect on Deformation Twin thickness in a nanocrystalline metal with low stacking fault energy
Journal of Materials Research, 2019Co-Authors: Liangjuan Dai, Yang Cao, Yonghao Zhao, Y T ZhuAbstract:Grain size effect on Twin thickness has been rarely investigated, especially when the grain size is less than 1000 nm. In our previous work (Mater. Sci. Eng. A527, 3942, 2010), different severe plastic Deformation techniques were used to achieve a wide range of grain sizes from about 3 µm to 70 nm in a Cu–30% Zn alloy. Transmission electron microscopy (TEM) revealed a gradual decrease in the Deformation Twin thickness with decreasing grain size. In the present work, high-resolution TEM was used to further identify Deformation Twins and measure their thickness, especially for grain sizes below 70 nm. The Twin thickness was found to gradually reduce with decreasing grain size, until a critical size (20 nm), below which only stacking faults were observed. Interestingly, the relationship between Twin thickness and grain size in the ultrafine/nanocrystalline regime is found similar to that in the coarse-grained regime, despite the differences in their Twinning mechanisms. This work provides a large set of data for setting up a model to predict the Twin thickness in ultrafine-grained and nanocrystalline face-centered cubic materials.
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strengthening at nanoscaled coherent Twin boundary in f c c metals
Philosophical Magazine, 2014Co-Authors: Ming Dao, Y T ZhuAbstract:This paper analyses slip transfer at the boundary of nanoscaled growth Twins in face-centred cubic (f.c.c.) metals for strengthening mechanism. The required stress for slip transfer, i.e. inter-Twin flow stress, is obtained in a simple expression in terms of stacking fault energy and/or Twin boundary (TB) energy, constriction energy and activation volume. For nanoTwinned Al, Cu and Ni, inter-Twin flow stress versus Twin thickness remarkably shows Hall–Petch relationship. The Hall–Petch slope is rationalized for various reactions of screw and non-screw dislocations at the TB. Additionally, strengthening at the boundary of nanoscaled Deformation Twins in f.c.c. metals is analysed by evaluating required Twinning stress. At small nanograin size, the prediction of Deformation Twin growth stress shows inverse grain-size effect on Twinning, in agreement with recent experimental finding.
Kaneaki Tsuzaki - One of the best experts on this subject based on the ideXlab platform.
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effect of strain rate on hydrogen embrittlement susceptibility of Twinning induced plasticity steel pre charged with high pressure hydrogen gas
International Journal of Hydrogen Energy, 2016Co-Authors: Motomichi Koyama, Gregory Gerstein, H J Maier, Kaneaki TsuzakiAbstract:Abstract The effects of tensile strain rate on the hydrogen-induced mechanical and microstructural features of a Twinning-induced plasticity (TWIP) steel were investigated using a Fe-23Mn-0.5C steel with a saturated amount of hydrogen. To obtain a homogeneous hydrogen distribution, high-pressure hydrogen gas pre-charging was performed at 423 K. Similar to previous studies on hydrogen embrittlement, the deterioration in the tensile properties became distinct when the strain rate was decreased from 0.6 × 10−3 to 0.6 × 10−4 s−1. In terms of microstructural features, hydrogen-precharging decreased the thickness of Deformation Twin plates, and it localized dislocation slip. Moreover, facets of the hydrogen-induced quasi-cleavage feature on the fracture surface became smoother with decreasing strain rate. In this study, we proposed that a combined effect of hydrogen segregation, slip localization, and thinning of Twin plates causes the hydrogen embrittlement of TWIP steels, particularly at a low strain rate.
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effect of Deformation Twin on toughness in magnesium binary alloys
Philosophical Magazine, 2015Co-Authors: Hidetoshi Somekawa, Tadanobu Inoue, Kaneaki TsuzakiAbstract:The impact of alloying elements on toughness was investigated using eight kinds of Mg-0.3 at.% X (X = Al, Ag, Ca, Gd, Mn, Pb, Y and Zn) binary alloys with meso-grained structures. These binary alloys had an average grain size of approximately 20 μm. The fracture toughness and crack propagation behaviour were influenced by the alloying elements; the Mg–Ag and Mg–Pb alloys had the highest and the lowest toughness amongst the alloys, respectively, irrespective of presence in their type Deformation Twins. The Twin boundaries affected the crack propagation behaviour in most of the alloys; in contrast, not only was the fracture related to the Twin boundaries, but also the intergranular fracture occurred in the alloys that included rare earth elements. The influential factor for toughness in the meso- and the coarse-grained magnesium alloys, which readily formed Deformation Twins during plastic Deformation, was not the change in lattice parameter with chemical composition, but the Twin boundary segregation energy.
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hydrogen induced cracking at grain and Twin boundaries in an fe mn c austenitic steel
Scripta Materialia, 2012Co-Authors: Dierk Raabe, Motomichi Koyama, Kaneaki Tsuzaki, Eiji Akiyama, Takahiro SawaguchiAbstract:Hydrogen embrittlement was observed in an Fe–18Mn–1.2C (wt.%) steel. The tensile ductility was drastically reduced by hydrogen charging during tensile testing. The fracture mode was mainly intergranular fracture, though transgranular fracture was also partially observed. The transgranular fracture occurred parallel to the primary and secondary Deformation Twin boundaries, as confirmed by electron backscattering diffraction analysis and orientation-optimized electron channeling contrast imaging. The microstructural observations indicate that cracks are initiated at grain boundaries and Twin boundaries.
Peter K Liaw - One of the best experts on this subject based on the ideXlab platform.
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atomistic simulations of the face centered cubic to hexagonal close packed phase transformation in the equiatomic cocrfemnni high entropy alloy under high compression
Computational Materials Science, 2020Co-Authors: Kangtien Hsieh, Peter K Liaw, Youyi Lin, Jerren Yang, Chinlung KuoAbstract:Abstract We performed the modified-embedded-atom-method (MEAM) based molecular dynamics (MD) simulations to investigate the plastic Deformation and phase transformation behaviors in the CoCrFeMnNi HEA under high compression at room temperature. Our MD simulations revealed that the stress-induced phase transformations in the CoCrFeMnNi HEA are strongly crystal orientation-dependent. The [0 0 1] uniaxial compression can induce the significant face-centered-cubic (fcc) -to-hexagonal-close-packed (hcp) phase transformation via successive emissions of partial dislocations from the extended stacking faults, Twin boundaries and hcp-lamellas created during the early stage of Deformation. As for the [1 1 0] and [1 1 1] uniaxial compressions, however, the transformed hcp atoms can simply form the intrinsic/extrinsic stacking faults. Although the [0 0 1] uniaxial compression produced a much lower dislocation density than the other two systems, it induced much more constituents transformed into the hcp atoms at the end of phase transformation. Our results clearly indicated that the Deformation Twin boundaries and extended hcp-lamellas play a critical role in facilitating the stress-induced fcc-to-hcp phase transformation in the CoCrFeMnNi HEA. Furthermore, it was found that the phase transformation in the CoCrFeMnNi HEA can be effectively facilitated by a large deviatoric compressive stress while it may tend to be significantly retarded by a hydrostatic compression. Our results also showed that the plastic Deformation behaviors in Ni under high compression are very similar to those occurred in the CoCrFeMnNi HEA though nearly all the hcp atoms can simply constitute the intrinsic/extrinsic stacking faults without the formation of any bulk hcp phase in the fcc lattice. The main discrepancy in the phase transformation behaviors between the Ni and CoCrFeMnNi HEA can be largely attributed to the much lower stacking fault energy of the CoCrFeMnNi HEA than other fcc metals.
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Deformation mechanisms of a 20mn twip steel investigated by in situ neutron diffraction and tem
Acta Materialia, 2013Co-Authors: Y F Shen, Y D Wang, Xiaopeng Liu, Xin Sun, Lin R Peng, S Y Zhang, Liang Zuo, Peter K LiawAbstract:Abstract The Deformation mechanisms and associated microstructure changes during tensile loading of an annealed Twinning-induced plasticity steel with chemical composition Fe–20Mn–3Si–3Al–0.045C (wt.%) were systematically investigated using in situ time-of-flight neutron diffraction in combination with post mortem transmission electron microscopy (TEM). The initial microstructure of the investigated alloy consists of equiaxed γ grains with the initial α′-phase of ∼7% in volume. In addition to dislocation slip, Twinning and two types of martensitic transformations from the austenite to α′- and e-martensites were observed as the main Deformation modes during the tensile Deformation. In situ neutron diffraction provides a powerful tool for establishing the Deformation mode map for elucidating the role of different Deformation modes in different strain regions. The critical stress is 520 MPa for the martensitic transformation from austenite to α′-martensite, whereas a higher stress (>600 MPa) is required for actuating the Deformation Twin and/or the martensitic transformation from austenite to e-martensite. Both e- and α′-martensites act as hard phases, whereas mechanical Twinning contributes to both the strength and the ductility of the studied steel. TEM observations confirmed that the Twinning process was facilitated by the parent grains oriented with 〈1 1 1〉 or 〈1 1 0〉 parallel to the loading direction. The nucleation and growth of Twins are attributed to the pole and self-generation formation mechanisms, as well as the stair-rod cross-slip mechanism.
Chinlung Kuo - One of the best experts on this subject based on the ideXlab platform.
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atomistic simulations of the face centered cubic to hexagonal close packed phase transformation in the equiatomic cocrfemnni high entropy alloy under high compression
Computational Materials Science, 2020Co-Authors: Kangtien Hsieh, Peter K Liaw, Youyi Lin, Jerren Yang, Chinlung KuoAbstract:Abstract We performed the modified-embedded-atom-method (MEAM) based molecular dynamics (MD) simulations to investigate the plastic Deformation and phase transformation behaviors in the CoCrFeMnNi HEA under high compression at room temperature. Our MD simulations revealed that the stress-induced phase transformations in the CoCrFeMnNi HEA are strongly crystal orientation-dependent. The [0 0 1] uniaxial compression can induce the significant face-centered-cubic (fcc) -to-hexagonal-close-packed (hcp) phase transformation via successive emissions of partial dislocations from the extended stacking faults, Twin boundaries and hcp-lamellas created during the early stage of Deformation. As for the [1 1 0] and [1 1 1] uniaxial compressions, however, the transformed hcp atoms can simply form the intrinsic/extrinsic stacking faults. Although the [0 0 1] uniaxial compression produced a much lower dislocation density than the other two systems, it induced much more constituents transformed into the hcp atoms at the end of phase transformation. Our results clearly indicated that the Deformation Twin boundaries and extended hcp-lamellas play a critical role in facilitating the stress-induced fcc-to-hcp phase transformation in the CoCrFeMnNi HEA. Furthermore, it was found that the phase transformation in the CoCrFeMnNi HEA can be effectively facilitated by a large deviatoric compressive stress while it may tend to be significantly retarded by a hydrostatic compression. Our results also showed that the plastic Deformation behaviors in Ni under high compression are very similar to those occurred in the CoCrFeMnNi HEA though nearly all the hcp atoms can simply constitute the intrinsic/extrinsic stacking faults without the formation of any bulk hcp phase in the fcc lattice. The main discrepancy in the phase transformation behaviors between the Ni and CoCrFeMnNi HEA can be largely attributed to the much lower stacking fault energy of the CoCrFeMnNi HEA than other fcc metals.